The invention relates to a data carrier for the contactless communication of communication information with a transmitting/receiving station, having receiving means for receiving an HF signal containing the communication information from the transmitting/receiving station, and having processing means for processing the received communication information, and having supply voltage generating means for rectifying the received HF signal and for energizing the processing means with a supply voltage, and having reset means for resetting, when the supply voltage decreases below a reset voltage value, the processing performed by the processing means.
Such a data carrier of the type defined in the opening paragraph is known from U.S. Pat. No. 5,736,728 and is formed by a transponder of a smart card. The known data carrier is adapted to provide contactless communication of communication information with a transmitting/receiving station. For this purpose, the data carrier has receiving means which include an antenna stage, a clock generation stage and a demodulation stage. By means of the antenna stage it is possible to receive an HF signal from the transmitting/receiving station, which signal may contain communication information in the form of modulated communication data. The clock generation stage is adapted to derive a clock signal from the HF signal and the demodulation stage is adapted to demodulate the modulated communication data received. The demodulated communication data are processed by processing means and, if necessary, stored in the data carrier.
The known data carrier further has supply voltage generating means adapted to rectify the received HF signal and to supply a supply voltage to the processing means. Since the known data carrier does not have a battery or other power source the processing means can process the received communication data only when the supply voltage has a sufficiently high voltage value.
The data carrier has reset means in order to guarantee a reliable processing of the communication data by the processing means. The reset means are adapted to reset the processing means and re-start the processing of the communication data by the processing means when the supply voltage decreases below a reset voltage value. Thus, it is precluded that the processing means carry out certain processing operations (for example, a storage operation) for whose reliable completion the supply voltage having the reset voltage value would be inadequate.
It has been found that the known data carrier has the disadvantage that the processing of the communication data by the processing means is interrupted comparatively often by a reset from the reset means and should be started virtually anew, although in certain cases this would not be necessary while the reliability with which the communication data are processed remains the same.
It is an object of the invention to provide a data carrier in which the processing by the processing means is reset only when this is absolutely necessary in order to maintain the reliability of the processed communication data. According to the invention, in order to achieve this object with a data carrier of the type defined in the opening paragraph, the reset means are adapted to interrupt the processing of the communication information by the processing means at least partially when the supply voltage decreases below an interruption voltage value, the interruption voltage value being greater than the reset voltage value.
Thus, it is achieved that the processing of the communication data by the processing means is merely interrupted for the time being and is resumed at the same stage of processing, for example after expiry of a given time interval. During the break in the processing the processing means consume hardly any power, for which reason the supply voltage generating means can generate the supply voltage with a voltage value which is adequate to maintain the processing status of the processing means even in the case of an HF signal having only a small amplitude.
This has the advantage that in certain cases, in which the data carrier is already comparatively far from the transmitting/receiving station and the amplitude of the HF signal is comparatively low, processing of the communication information with interruptions is possible altogether and can also be effected without unnecessary delays by a reset of the processing means.
It is to be noted that from the document WO99/50738 a data carrier is known which has pause detection means for the detection pause intervals in which the amplitude-modulated HF signal has a lower amplitude. The pause detection means are adapted to interrupt the processing of the processing means in pause intervals. However, the aforementioned object cannot be achieved with these pause detection means because the supply voltage depends not only on the amplitude of the HF signal but also very strongly on the instantaneous power consumption of the processing means and on further factors of influence that cannot be determined with the aid of the known pause detection means. Such influence factors are the temperature dependence and the load dependence of the supply voltage generated by the supply voltage generating means, which also depends on tolerances of the components of the supply voltage generating means.
The measures defined in claim 2 have the advantage that the processing of the communication information by the processing means is resumed only when the supply voltage generating means supply an adequate supply voltage which is unlikely to be followed directly by another interruption.
The measures defined in claim 3 have the advantage that, when the break in the processing of the communication information by the processing means has become too long and the data stored temporarily in the processing means are no longer reliable, processing is not resumed but is restarted by a reset.